1. Field of the Invention
The present invention relates to an automatic focusing apparatus which is suitably used in video equipment comprising image pickup means such as a video camera, and performs automatic focusing control using an image pickup signal output from the image pickup means.
2. Related Background Art
Video equipment comprising image pickup means such as a video camera adopts an automatic focusing (AF) system wherein a predetermined signal component, which changes in correspondence with a focusing state, is extracted from an image pickup signal output from the image pickup means, and the extracted signal component is used as an evaluation signal of the focusing state.
For example, an AF apparatus based on a so-called xe2x80x9chill-climbing AF systemxe2x80x9d is known. In the hill-climbing AF system, a high-frequency component indicating sharpness of an image is extracted from an image pickup signal output from an image pickup element such as a CCD, and a focusing lens is driven to maximize the level of the extracted high-frequency component, thus achieving AF control.
FIG. 1 shows the arrangement of a conventional AF apparatus based on the xe2x80x9chill-climbing systemxe2x80x9d.
Referring to FIG. 1, a focusing lens 1 is moved by a lens driving motor 57 in the optical axis direction to achieve a focusing operation. Light transmitted through the focusing lens 1 forms an image on the image pickup surface of an image pickup element 3, the formed image is photoelectrically converted into an electrical image pickup signal, and the image pickup signal is output. The image pickup signal is sampled and held by a CDS (double correlation sampling circuit)/AGC (auto-gain control circuit) 4, and is amplified to a predetermined level. Thereafter, the image pickup signal is converted into a digital image pickup signal by an A/D converter 5. The digital image pickup signal is input to a process circuit of a camera, and is converted into a standard television signal based on the NTSC system. The digital image pickup signal is also input to a band-pass filter (to be referred to as a BPF hereinafter) 100.
The BPF 100 extracts a high-frequency component from the image pickup signal, and a gate circuit 101 extracts only a signal corresponding to a portion set to be an in-focus detection region in a photographing field. A peak hold circuit 102 holds a peak value of the output from the gate circuit 101 at an interval synchronous with an integer multiple of a vertical synchronization signal. Since this peak hold value is utilized in AF control, it will be referred to as an AF evaluation value hereinafter.
A speed discrimination circuit 104 sets a focusing speed corresponding to an in-focus degree on the basis of the AF evaluation value. More specifically, the circuit 104 instructs a motor driver 56 to vary the motor speed, so that the motor speed is increased in a considerably out-of-focus state, and the motor speed is decreased in a slightly out-of-focus state. On the other hand, a direction discrimination circuit 103 sets the motor driving direction in a direction to increase the AF evaluation value, thereby increasing the in-focus degree. Such control is the above-mentioned hill-climbing control.
In the conventional AF apparatus based on the hill-climbing system, since AF control is performed using only a focus detection signal extracted from only one focus detection region set in the photographing field, the AF operation becomes unstable depending on objects and photographing conditions.
In order to realize the above-mentioned AF apparatus using the image pickup signal, many means such as means for extracting an evaluation signal, which changes in correspondence with a focusing state, from an image pickup signal, means for setting a detection region in a photographing field for obtaining the evaluation signal, arithmetic and control means for executing a control algorithm for driving a focusing lens on the basis of the evaluation signal, means for controlling the operation timing with other circuits other than those associated with an AF function, and the like are required. For this reason, the circuit arrangement, and various setting and adjustment operations as a whole are complicated. Also, use of both analog and digital circuits disturbs efficient signal processing, and undesirably allows easy mixing of noise. Thus, the AF apparatus suffers from many problems including the above-mentioned problems, and it is difficult to realize a stable, efficient, and high-precision AF apparatus.
In particular, in a focus detection apparatus using an image pickup signal, since a dynamic image is to be picked up, a detection region corresponding to a change in image must be set, and a focus detection algorithm corresponding to a change in image must be executed. However, it is very difficult to realize these operations by the above-mentioned circuit arrangement. Therefore, demand has arisen for practical means which can efficiently and stably control circuit operations, can simplify the circuit arrangement, and allows easy connections with other control circuits to improve efficiency of the entire system.
The present invention has been made to solve the above-mentioned problems, and has as its first object to realize high efficiency, simplification, and high reliability of control of various functions necessary for realizing an AF function.
It is the second object of the present invention to improve efficiency and versatility of processing by forming a one-chip IC including circuits for realizing various functions for executing the AF function.
In order to solve the above-mentioned problems, according to one preferred aspect of the present invention, there is disclosed a focus signal control integrated circuit comprising at least: gate means for extracting only an image pickup signal corresponding to a portion inside a predetermined detection region in a photographing field, and capable of changing a setting position of the detection region in the photographing field; filter means for extracting a predetermined frequency component, which changes in correspondence with a focusing state, from the image pickup signal extracted by the gate means; arithmetic means for generating an evaluation signal of the focusing state by executing predetermined processing of the predetermined signal component extracted by the filter means; region setting means for controlling the position or the number of focus detection regions in the photographing field by controlling the gate means; and interface means for allowing external control of the respective means.
Thus, various functions necessary for AF control can be integrated on a one-chip IC, the position or the number of focus detection regions in the photographing field can be freely set by an external control command, the operations of various functions can be controlled in correspondence with a photographing state, and timing control with other functions is facilitated. Therefore, a one-chip IC for an AF apparatus, which can satisfy various requirements from the system design, can be realized.
It is the third object of the present invention to disclose an automatic focus detection apparatus which can solve a conventional problem that focus detection precision deteriorates due to a change in object image and photographing conditions to cause an erroneous operation in an apparatus for performing focus detection on the basis of an image pickup signal in a single fixed focus detection region set in a photographing field, and allows a stable AF operation all the time despite a change in object image and photographing conditions without causing any erroneous operation.
In order to achieve the above object, according to another preferred aspect of the present invention, there is disclosed an automatic focus detection apparatus comprising: filter means for extracting a predetermined frequency component from an image pickup signal output from image pickup means; gate means for allowing only a signal corresponding to a portion in a focus detection region in a photographing field to pass therethrough with respect to the output from the filter means; detection means for detecting a luminance signal component from the image pickup signal in the focus detection region; correction means for correcting a focus signal extracted by the gate means by the output from the detection means; and driving means for driving a focusing lens of an optical system to an in-focus point on the basis of the output signal from the correction means.
In order to achieve the above object, according to still another preferred aspect of the present invention, there is disclosed an automatic focus detection apparatus comprising: filter means for extracting a predetermined frequency component from an image pickup signal output from image pickup means; gate means for movably setting a plurality of focus detection regions in a photographing field with respect to the output from the filter means, and allowing signals corresponding to portions in the focus detection regions to pass therethrough; detection means for detecting luminance signal components from the image pickup signals in the respective focus detection regions; correction means for correcting focus signals extracted by the gate means by the outputs from the detection means; and driving means for driving a focusing lens of an optical system to an in-focus point on the basis of the output signals from the correction means.
It is the fourth object of the present invention to improve the performance of a conventional xe2x80x9chill-climbing AF system,xe2x80x9d and to provide an automatic focus detection apparatus which can fetch an evaluation signal of a focusing state at a shorter period, can shorten a time lag between the current image signal and AF control, and can realize high-precision, high-speed, and stable AF control.
In order to achieve the above object, according to still another preferred aspect of the present invention, there is disclosed an automatic focus detection apparatus comprising: a plurality of band-pass filters each for extracting a predetermined focus signal, which changes in correspondence with a focusing state, from an image pickup signal output from image pickup means; switching means for switching the band-pass filters; horizontal direction detection means for detecting an output level of the band-pass filter in synchronism with a horizontal synchronization signal; and peak hold means for holding a peak value of an output from the horizontal direction detection means.
It is the fifth object of the present invention to provide an AF apparatus which can prevent an out-of-focus image from being recorded, by redriving an AF operation when a recording standby state transits to a recording state.
It is the sixth object of the present invention to provide an AF apparatus which can attain a quick focusing operation by driving a focusing lens in a direction determined based on the position of the focusing lens and a predetermined standard object position when the driving direction of the focusing lens cannot be discriminated on the basis of the focus signal level.